Method of reducing drag on the outer surface of a vehicle

ABSTRACT

A vehicle with a drag-reducing outer surface. A method of reducing aerodynamic or hydrodynamic drag on a vehicle includes the steps of: providing an outer surface on a body of the vehicle, with the outer surface including spaced apart turbulence-inducing structures thereon. The structures cause boundary layer separation to be delayed along a length of the body, thereby reducing a drag coefficient of the body. A vehicle wrapping product for reducing aerodynamic or hydrodynamic drag on a vehicle includes an outer surface for applying onto an opaque portion of a body of the vehicle. The outer surface includes a plurality of structures which induce turbulence and thereby delay separation of a boundary layer along a length of the body, to thereby reduce a drag coefficient of the body.

This application claims priority to the following U.S. PatentApplication which is incorporated by reference herein in its entirety:U.S. patent application Ser. No. 12/102,668, filed Apr. 14, 2008entitled “Vehicle with Drag-Reducing Outer Surface.”

BACKGROUND

The present disclosure relates generally to the art of providing moreefficient vehicles and, in an embodiment described herein, moreparticularly provides a vehicle with a drag-reducing outer surface.

A vehicle in motion through a fluid (liquid or gas, such as air) createsdrag, which tends to resist the motion of the vehicle. Thus, drag slowsthe motion of the vehicle, or requires the use of increased energy tomaintain or increase a speed of the vehicle.

In the past, vehicle designers have attempted to reduce the effects ofdrag on vehicles by shaping the vehicles so that less frontal area isexposed to the fluid, and/or so that the extent of a laminar boundarylayer is maximized. These techniques are well known to those skilled inthe arts of aerodynamics and hydrodynamics.

However, not all vehicles can be shaped like sports cars or high speedboats. Furthermore, it is uneconomical or otherwise undesirable tochange the overall shape of an existing vehicle.

Therefore, it may be seen that improvements are needed in the art ofreducing the drag coefficient of a vehicle. Such improvements wouldallow increased speed at a given level of energy expenditure, or wouldallow operation at a given speed while reducing the required energyexpenditure.

SUMMARY

In the present specification, a technique is provided which solves atleast one problem in the art. One example is described below in whichdrag is reduced by incorporating a turbulent boundary layer adjacent anouter surface of a body of a vehicle. Another example is described belowin which the outer surface is provided on a vehicle wrapping product.

In one aspect, a method of reducing aerodynamic or hydrodynamic drag ona vehicle is provided. The method includes the steps of: providing anouter surface on a body of the vehicle, the outer surface includingspaced apart turbulence-inducing structures thereon; and whereby thestructures cause boundary layer separation to be delayed along a lengthof the body, thereby reducing a drag coefficient of the body.

In another aspect, a vehicle wrapping product for reducing aerodynamicor hydrodynamic drag on a vehicle is provided. The wrapping productincludes an outer surface for applying onto an opaque portion of a bodyof the vehicle. The outer surface includes a plurality of structureswhich induce turbulence and thereby delay separation of a boundary layeralong a length of the body, to thereby reduce a drag coefficient of thebody.

These and other features, advantages, benefits and objects will becomeapparent to one of ordinary skill in the art upon careful considerationof the detailed description of representative embodiments hereinbelowand the accompanying drawings, in which similar elements are indicatedin the various figures using the same reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a prior art vehicle;

FIG. 2 is a side view of a vehicle which incorporates principles of thepresent disclosure;

FIG. 3 is an enlarged scale schematic view of a turbulent boundary layeron the vehicle of FIG. 2;

FIG. 4 is a reduced scale outer view of a wrapping product for use onthe vehicle of FIG. 2;

FIG. 5 is an enlarged scale schematic cross-sectional view of thewrapping product on the vehicle of FIG. 2; and

FIG. 6 is an enlarged scale schematic cross-sectional view of thewrapping product of FIG. 5 having an additional outer layer thereon.

DETAILED DESCRIPTION

It is to be understood that the various embodiments described herein maybe utilized in various orientations, such as inclined, inverted,horizontal, vertical, etc., and in various configurations, withoutdeparting from the principles of the present disclosure. The embodimentsare described merely as examples of useful applications of theprinciples of the disclosure, which are not limited to any specificdetails of these embodiments.

In the following description of the representative embodiments of thedisclosure, directional terms, such as “above”, “below”, “upper”,“lower”, etc., are used for convenience in referring to the accompanyingdrawings. In general, “above”, “upper”, “upward” and similar terms referto a vertical direction ascending from the earth's surface, and “below”,“lower”, “downward” and similar terms refer to a vertical directiondescending from the earth's surface.

Representatively illustrated in FIG. 1 is a prior art vehicle 10. Whenthe vehicle 10 moves forward relative to a fluid (such as air), a“flowfield” 12 is created about the vehicle.

In general, a laminar boundary layer 14 is formed adjacent a smallportion of a body 16 of the vehicle 10. However, this laminar boundarylayer 14 is easily disrupted by, for example, changes in contour of thebody 16. In FIG. 1, the boundary layer 14 separates from the body 16 ata point of separation 18 which is located at an upper edge of awindshield 20 of the vehicle 10.

In many cases, the point of separation 18 occurs where the maximumthickness of the vehicle 10 begins. In nearly all cases, turbulence iscreated when the Reynolds number is over about 2-3.times.10.sup.5.

Downstream of the point of separation 18, a relatively large turbulentwake 22 is formed in the flowfield 12. Pressure in this wake 22 isreduced relative to pressure in the flowfield 12 upstream of the pointof separation 18. As a result, a pressure differential is created acrossthe vehicle 10, which pressure differential tends to hinder forwardmotion of the vehicle.

This principle is embodied in the well-known equation for aerodynamicdrag as follows:Drag=(1/2)ru.sup.2C.sub.dA  (1)

wherein r is fluid density, u is fluid velocity, C.sub.d is thecoefficient of drag, and A is frontal area.

Based on this equation, for a given fluid density and velocity, drag canbe reduced by reducing the coefficient of drag, and by reducing thefrontal area of a vehicle. If it is impractical or otherwise undesirableto reduce the frontal area of the vehicle, then drag can still bereduced by reducing the coefficient of drag.

At the Reynolds numbers typically found in vehicle motion (e.g., Re<1.times.10.sup.4), viscous forces dominate the flow, and skin frictiondrag is less significant. Therefore, the coefficient of drag at lowerReynolds numbers can be substantially reduced without much concern forhow skin friction is affected.

Referring additionally now to FIG. 2, a vehicle 30 embodying principlesof the present disclosure is representatively illustrated. In overallshape, the vehicle 30 is very similar to the prior art vehicle 10,however, the vehicle 30 of FIG. 2 includes important features whichsubstantially reduce its coefficient of drag.

Note that a flowfield 32 is created in the fluid surrounding the vehicle30, and that a laminar boundary layer 34 is formed adjacent a body 36 ofthe vehicle, similar to those for the vehicle 10 of FIG. 1. However, apoint of separation 38 of the boundary layer for the vehicle 30 of FIG.2 is located much farther downstream along the length of the body 36 ascompared to the point of separation 18 for the vehicle 10 of FIG. 1.

As a result, the turbulent wake 40 is much smaller for the vehicle 30 ofFIG. 2. This smaller wake 40 produces a decreased pressure differentialacross the body 36, and the coefficient of drag for the vehicle 30 issignificantly reduced.

This result is achieved by providing a turbulent boundary layer 42adjacent the body 36 of the vehicle 30. Specifically, the laminarboundary layer 34 is “tripped” into turbulence at a tripping point 44,which causes the boundary layer to remain adjacent the outer surface ofthe body for a greater distance downstream along the length of the body36, thereby delaying separation of the boundary layer from the body.

Referring additionally now to FIG. 3, an enlarged scale view of theturbulent boundary layer 42 is representatively illustrated. In thisview it may be seen that turbulence-inducing structures 46 are providedon an outer surface 48 of the vehicle 30 exposed to the flowfield 32.

The structures 46 function to induce turbulence in the boundary layer 42at Reynolds numbers much less than 2-3.times.10.sup.5. Theseturbulence-inducing structures 46 create the high energy turbulentboundary layer 42, which is much more able to resist the adversepressure gradients present in the flowfield 32 about the body 36 ascompared to the laminar boundary layer 34. Consequently, the point ofseparation 38 is displaced substantially rearward of the onset ofmaximum thickness of the body 36.

As depicted in FIG. 3, the structures 46 comprise upstanding elements onthe body 36 of the vehicle 30. However, the turbulence-inducingstructures could instead be recesses on the body 36. Furthermore, thestructures could be integrally formed with the body 36, or they could beapplied to the body after the body is manufactured.

As an example of the latter alternative, in FIG. 4 a vehicle wrappingproduct 50 is representatively illustrated, apart from the vehicle 30.This wrapping product 50 is configured to be applied to the body 36after the body is manufactured. For example, the wrapping product 50could be applied to an existing vehicle, or the wrapping product couldbe applied to the body 36 as part of the vehicle manufacturing process.

The wrapping product 50 is provided in sheets (preferably rolled up forconvenient transport and handling). Perforations 52 are formed in thesheets to provide the turbulence-inducing structures 46 on an outersurface 54 of the wrapping product 50.

Referring additionally now to FIG. 5, an enlarged scale cross-sectionalview of one example of the wrapping product 50 is representativelyillustrated. In view, the wrapping product 50 has been adhesivelysecured onto the body 36 of the vehicle 30.

As depicted in FIG. 5, the wrapping product 50 includes a perforatedlayer 56 in which the perforations 52 are formed. The perforations 52are preferably dimensioned and appropriately spaced apart so that theturbulent boundary layer 42 is formed adjacent the body 36 when the bodyis in motion through the flowfield 32.

For example, the perforations 52 preferably have a diameter ofapproximately 0.17 inch, are offset 60% line-to-line, and are spaced 1inch center-to-center between vertically aligned perforations asdepicted in FIG. 5. However, it should be clearly understood that otherdiameters, offsets and spacings may be used, and other shapes ofperforations (such as squares, hexagons, octagons, ovals, etc.) may beused, without departing from the principles of this disclosure.

The perforated layer 56 is preferably made of an opaque vinyl material,with an adhesive 58 on one side for adhering the layer onto the body 36.The perforated layer 56 may also be provided with channels on itsunderside for releasing air from between the body and the perforatedlayer when the perforated layer is adhered onto the body 36.

The material of which the perforated layer 56 is made may beconventional vehicle wrap material designed for use on non-glasssurfaces of vehicles. This material may then be perforated to form theperforated layer 56.

The wrapping product 50 is preferably applied only to opaque non-glassportions 31 of the body 36 (as opposed to the glass portions 33). Forexample, the wrapping product 50 may be applied to rigid metal or moldedplastic portions of the body. In addition, the wrapping product 50 ispreferably applied to at least 20% of the exterior of the body forminimal effectiveness, is more preferably applied to at least 30% of theexterior of the body for increased effectiveness, and is most preferablyapplied to all opaque portions of the body 36 for maximum effectiveness.

One beneficial feature of the wrapping product 50 is that the body 36can be viewed from an exterior of the perforated layer 56 through theperforations 52. This provides an additional aesthetic designopportunity.

For example, the perforated layer 56 could be provided in a color whichcontrasts with or complements a color of the body 36. Alternatively, theperforated layer 56 could be provided in a clear material, in which casethe color of the body 36 could be visible through the material of theperforated layer.

Referring additionally now to FIG. 6, a schematic cross-sectional viewof a more preferred version of the wrapping product 50 isrepresentatively illustrated. In this version, another layer 60 isprovided over the perforated layer 56.

Preferably, the outer layer 60 is made of a laminate (a clear vinylmaterial), so that the perforated layer 56 and the body 36 are visiblethrough the layer 60. However, it will be appreciated that it is notnecessary for the layer 60 to be clear in keeping with the principles ofthis disclosure.

If the outer layer 60 is made of a laminate, the laminate is preferablynot optically-clear as that term is understood in the vehicle wrappingindustry. Instead, since the wrapping product 50 is preferably appliedto opaque portions of the body 36, the layer 60 can be made of materialwhich is less expensive than optically-clear material.

The outer layer 60 is preferably made of a conventional laminatematerial which is designed for use on non-glass surfaces of vehicles(known to those skilled in the art as vehicle wrap laminate). Thisvehicle wrap laminate material is clear, but is not optically-clear.

The outer layer 60 is preferably laminated with the perforated layer 56prior to applying the wrapping product 50 to the vehicle 30. However,the outer layer 60 could be applied on the perforated layer 56 after theperforated layer has been applied to the body 36, if desired.

Recesses 62 are formed in the outer layer 60 when the outer layer islaminated or otherwise applied onto the perforated layer 56. That is,the material of the outer layer 60 extends into the perforations 52,thereby forming the recesses 62.

In this configuration, the recesses 62 comprise the structures 46 whichinduce turbulence in the boundary layer 42. Note that, instead of or inaddition to the recesses 62, projections or other types ofturbulence-inducing structures may be formed on the wrapping product 50in keeping with the principles of this disclosure.

Although an automobile has been used herein as an example of a vehiclewhich can incorporate principles of this disclosure, it will beappreciated that other types of vehicles can also incorporate principlesof this disclosure. For example, boats and any other type of vehiclewhich would benefit from a reduction in drag coefficient may incorporateprinciples of this disclosure.

It may now be fully appreciated that the above disclosure provides manybenefits to the art of reducing drag in vehicles. These benefits areachieved in an economical manner, without requiring substantial changesto the overall shape of a vehicle, and can be useful for existing andnewly manufactured vehicles.

In one aspect, a method of reducing aerodynamic or hydrodynamic drag ona vehicle 30 is provided by this disclosure. The method includes thesteps of: providing an outer surface 48, 54 on a body 36 of the vehicle30, the outer surface 48, 54 including spaced apart turbulence-inducingstructures 46, 52, 62 thereon. The structures 46, 52, 62 cause boundarylayer separation to be delayed along a length of the body 36, therebyreducing a drag coefficient of the body 36.

The body 36 may be rigid. The rigid body 36 may comprise a metalmaterial.

The outer surface 48, 54 providing step may include applying aperforated layer 56 on an exterior of the body 36. The body 36 may beopaque.

The applying step may include applying the perforated layer 56 on anon-glass portion of the body 36. The exterior of the body 36 may bevisible through perforations 52 in the perforated layer 56.

The providing step may include applying a laminate 60 over theperforated layer 56. The applying step may include applying theperforated layer 56 on at least 20% or 30% of the exterior of the body36.

Also provided by the above disclosure is a vehicle wrapping product 50for reducing aerodynamic or hydrodynamic drag on a vehicle 30. Thewrapping product 50 includes an outer surface 48, 54 for applying ontoan opaque portion of a body 36 of the vehicle 30. The outer surface 48,54 includes a plurality of structures 46, 52, 62 which induce turbulenceand thereby delay separation of a boundary layer 42 along a length ofthe body 36, to thereby reduce a drag coefficient of the body 36.

The structures 46, 52, 62 may be dimensioned in a manner that aturbulent boundary layer 42 is created adjacent the outer surface 48, 54when the body 36 displaces relative to a fluid 29.

The outer surface 48, 54 may be formed on a laminate 60. The wrappingproduct 50 may also include a perforated layer 56 adjacent the laminate60.

Each of the laminate 60 and the perforated layer 56 may comprise a vinylmaterial. The perforated layer 56 may be opaque. The perforated layer 56may include perforations 52 therein, with each perforation having adimension of approximately 0.19 inch.

The structures 62 may be due to the laminate 60 being recessed intoperforations 52 in the perforated layer 56.

The wrapping product 50 may include a perforated layer 56 havingperforations 52 therein dimensioned in a manner that a turbulentboundary layer 42 is created adjacent the outer surface 48, 54 when thebody 36 displaces relative to a fluid.

The structures 46, 52, 62 may be dimensioned in a manner that theboundary layer is tripped from laminar 34 to turbulent 42 when the body36 displaces relative to a fluid.

Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments,readily appreciate that many modifications, additions, substitutions,deletions, and other changes may be made to these specific embodiments,and such changes are within the scope of the principles of the presentdisclosure. Accordingly, the foregoing detailed description is to beclearly understood as being given by way of illustration and exampleonly, the spirit and scope of the present invention being limited solelyby the appended claims and their equivalents.

1. A method of reducing drag resistance for a vehicle moving through afluid, the vehicle having a body with an outer surface having one ormore non-glass portions, the method comprising the steps of: providing aperforated sheet material having a plurality of perforations configuredto induce turbulence in the fluid flowing over the vehicle; providing asecond sheet material; applying the second sheet material to theperforated sheet material to form an outer layer; and applying theperforated sheet material to the non-glass portions of the body of thevehicle.
 2. The method of claim 1, wherein the second sheet material istransparent such that a portion of the outer surface of the body isvisible through perforations in the perforated sheet material.
 3. Themethod of claim 1, wherein the applying step further comprises applyingthe perforated sheet material to a majority of the non-glass portions ofthe body.
 4. The method of claim 1, wherein the vehicle is anautomobile.
 5. The method of claim 1, wherein a non-glass portion of thebody comprises a metal material.
 6. The method of claim 1, wherein anon-glass portion of the body is opaque.